The embodiment relates to a wireless power transmitter, a wireless power receiver, and a power transmission method of a wireless power transmission system.
A wireless power transmission or a wireless energy transfer refers to a technology of wirelessly transferring electric energy to desired devices. In the 1800's, an electric motor or a transformer employing the principle of electromagnetic induction has been extensively used and then a method for transmitting electrical energy by irradiating electromagnetic waves, such as radio waves or lasers, has been suggested. Actually, electrical toothbrushes or electrical razors, which are frequently used in daily life, are charged based on the principle of electromagnetic induction. Until now, the long-distance transmission using the magnetic induction, the resonance and the short-wavelength radio frequency has been used as the wireless energy transfer scheme.
Recently, among wireless power transmitting technologies, an energy transmitting scheme employing resonance has been widely used.
Since an electric signal generated between the wireless power transmitter and the wireless power receiver is wirelessly transferred through coils in a wireless power transmitting system using resonance, a user may easily charge electronic appliances such as a portable device.
An example of the wireless power transmitting technology is described in Korean Unexamined Patent Publication No. 10-2006-0031526, entitled “Bidirectional chargeable wireless charging pad and battery pack”, which implements a separating type transformer having a simple structure and a high coupling coefficient to detect a portable device or the battery pack mounted on a top surface of the wireless charging pad, and to monitor and control a charged state based on the detection result.
However, since impedance of a load side connected to a receiver side or inductance of a coil of the receiver side is fixed, a coupling state between a transmitter side and the receiver side varies so that power transmission efficiency is degraded.